Official Pentax K to Q lens adapter

Started Aug 25, 2011 | Discussions thread
godfrog Senior Member • Posts: 1,463
Re: Official Pentax K to Q lens adapter

MightyMike wrote:

godfrog wrote:

Not sure about the resolution being miserable, without including NR the resolution should be that of the capability of the lens itself assuming the sensor out resolves the lens.

That is true, the sensor will be the limit. But, if a stellar lens resolves 100lp/mm (at some contrast), then that is great on a sensor that is APS-C 24mm wide, 2400 line pairs resolved along the width. On a 1/2.3", 6mm wide, you'd resolve 600 line pairs along the width.

focus throw will be super short, mechanical tolerances much wider than what is used on 1/2.3" sensors,

Hold on here, a larger sensor requires finer tolerances for more precision, i believe therefore it will be the other way around. BTW the focus throw of the 77 is 120 degrees, the focus throw of my 100-300mm F4 is about 60 degrees... the focus throw doesn't change because you're on a different sized sensor

Smaller sensors most certainly require finer tolerances. Try using a 8x10 view camera and you'll notice that moving a lens 1mm one way or the other won't change much, while the same movement on a APS-C sensor camera will throw your image way out of focus.

Regarding focus throw, the throw will not change, but while a (theoretical) 280/6.7 lens designed for manual focus on APS-C would have a very long throw to take it from infinity focus to say 1.5m, a FA77/1.8 would have a much shorter throw to take it from infinity to 0.7m.

If you have a FA50/1.4 and a camera with live view, you can see what I mean. Zooming the live view to 4x will give you about the same view as the Q will. You'll notice small focus ring movements throw the image out of focus faster as you zoom further in. On APS-C you might use 10x to fine tune focus. 10x on a Q would be a view as narrow as 40x on an APS-C...

internal reflections from the lack of mechanical vignetting will zap contrast,

If this were true then the centers of all our photos would be equally bad regardless of the sensor size

Well yes, at F1.8, the contrast is quite low in the center, and of course, the entire image when shooting on APS-C. You'd probably be shooting at F5.6 if you wanted good contrast, and there would be no problems doing so. If you did that on the Pentax Q, you'd be loosing a lot of detail to diffraction, and you are now shooting an FF equivalent to 431mm without image stabilization on a camera that drops of in image quality much quicker than an APS-C as you start raising ISO to keep decent shutter speeds. DOF would be equal to the FF lens at F32...

Using lenses with way oversized image circles is not a good idea...

and you'll have a lot less dynamic range in scenes where there is enough light to use base ISO on the APS-C camera.

Hmmm... maybe a lot less then 14.5 stops but looking at DXO for comparison sake we could expect 10-11 stops and that similar to what we were getting just a few years back on DSLRs,

I'm pretty sure I do not want to go back to that But I know many people care less than me about dynamic range.

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